One certain type of conventional prior art load-setting system that is represented by load-compensation mechanisms is described in "100-type Railroad Brakes for New Speedy Railroad Cars of Tobutetsudo Railroad", pp. 22-29, Nabuko Technical Report No. 71, issued Jan. 1, 1991.
It should be particularly noted here that a block diagram of a brake system such as is presently being used in a generally known load-compensation device is illustrated in FIG. 3. The explanation to follow first considers a brake system designed to employ such known load-compensation device.
This brake system makes simultaneous use of both electric brakes, namely (regenerative brakes), and pneumatic brakes. Such known brake system is operated in such a manner that should an electric brake force which is developed under the effect of a braking command electrical signal value be insufficient, the system will then compensate for such brake force insufficiency by applying a supplemental pneumatic brake force.
As illustrated in FIG. 3, the brake command electrical signal value is supplied to a brake control unit 20 through a brake command communication line 10b. The brake control unit 20 calculates a brake command signal and a load command signal from a load compensation device 24 and communicates a regenerative brake command electrical signal to a power-running unit 21. This action results in a regenerative braking force being developed by a main circuit motor 34 disposed on such railway car.
Thus, a regenerative brake equivalence electrical signal can be developed by the above-mentioned regenerative brake from the power-running unit 21 which, according to this known brake system, calculates the compensation pneumatic braking force required and communicates an electrical pneumatic brake signal to a brake control device 22.
The electrical pneumatic brake signal is then converted by the brake control device 22 into a pneumatic pressure which is communicated to a brake cylinder 37. As is known in the railway car braking art, brake cylinder 37 applies a compensation braking force to the wheels of such railway car.
Furthermore, a power-running command electrical signal is applied to a power-running control unit 21 by a power-running command electrical signal communication line 10a. The power-running control unit 21 calculates the above-mentioned power-running command electrical signal and the load electrical signal 16 which is received from the load-compensation unit 24 through the brake control unit 20 and transmits the power-running electrical signal to the main circuit motor 34 which accelerates such railway car.
In FIG. 3, reference numeral 23 designates a slippage prevention device while reference numeral 6 designates a slippage detection controller. Reference numeral 9 identifies a speed-sensor device.
The description to follow primarily concerns the load-compensation device 24 and a load-detection device 46. A pneumatic spring 26 disposed on such railway car senses weight of the passengers and/or freight being transported on such railway car. The pneumatic spring 26 compresses in proportion to the weight and such railway car lowers toward the platform 42.
The lowering of the railcar body 43 is detected in this system by a control valve device 25. The control valve device 25 is also equipped to detect the vertical position of such railroad car body 43. An air inlet port of the control valve device 25 is for returning the railcar body 43 to its normal or initial position. Opening of the air inlet port of control valve device 25 permits a pressure buildup in the pneumatic spring 26 which results in such railcar body 43 returning to its initial position. At this point, the magnitude of increase in the pneumatic pressure present in the pneumatic spring 26 is substantially proportional to the load weight of the passengers or freight carried by such railroad car.
The pneumatic pressure within the pneumatic spring 26 is detected, in this prior art brake system, by a pneumo-electric converter (not shown) and is converted therein into an electrical signal value. This electrical signal value is amplified by an amplifier (not shown). The resulting amplified electrical signal is communicated to the load-compensation unit 24 and along with other electrical signals representative of various additional functions such as empty-car verification is communicated to the brake control unit 20 as the load electrical signal 16.
A problem arises with this prior art brake system, however, when such railway car is not equipped with the pneumatic spring 26. In this event, the load compensation device 24 and the load detection device 46 cannot detect pneumatic pressure. Furthermore, even if the pneumatic spring 26 is used, on such railway cars in which pneumatic pressure within the pneumatic spring 26 is utilized to perform another purpose, the pneumatic spring 26 pressure will not necessarily be proportional to the weight of the passengers and/or freight. The pneumatic spring 26 may, for example, be utilized to control the side to side tilting of such railway car which is equipped with a pendulum-type support structure. In this case, the pneumatic spring 26 ensures positive tilt of such railway car body 43 towards the inner side as a means of reducing centrifugal force being exerted as such railway car is propelled at a high speed along a curved portion of a track.
Under these circumstances, when air pressure present in the pneumatic spring 26 becomes substantially non-proportional to the weight of the passengers, the load electrical signal therefore does not accurately represent the weight of the passengers. In this case such railway car is constructed in a manner such that the required speed of acceleration and/or deceleration of such railway car is constant and does not depend on a certain amount or weight of passengers. The power-running command electrical signal communicated by a train operator and the brake command electrical signal are therefore affected by the weight of such railcar body 43 and such railway car accelerates or decelerates in response to the train operator's commands.
As this does not accurately reflect the actual load conditions, however, it is extremely difficult for the train operator to control acceleration and deceleration of such railway car. Consequently, this prior art control system requires the train operator to be extremely versatile and highly skilled in train operation techniques.